Referring to FIG. 1, it is known to provide a desktop battery charger station 1 having a first slot 2, sometimes referred to as a "front-slot", for receiving a cellular telephone 6 and a second slot 3, sometimes referred to as a "back-slot", for receiving just a battery module or pack 5 of the cellular telephone. In this manner the user is enabled to recharge the battery pack that is currently installed within the phone 6 by inserting the base of the phone 6 into the first slot 2, while a spare battery pack 5 is installed within the second slot 3. A connection 4 is provided for coupling the charger station 1 to a source of electric power. The charger station 1 can contain a PWM circuit for selectively applying charging pulses to the phone's battery pack and to the back-slot battery pack. Alternatively, PWM signals can be obtained from the charging circuitry (CC) 7 contained within the phone 6. Some phones are also known that contain a switch (SW) in series with the battery, where the switch is opened and closed by the charging circuit 7 at, for example, a 1 Hz rate. When the switch is closed the charger 1 provides current to the battery, and when the switch is opened no current is drawn from the battery of the phone 6.
It is not required that both slots 2 and 3 be used simultaneously, as one slot or the other could be used at any given time.
However, this arrangement is not always optimum, as the conventional operation shares the charger station 1 by defining a charging time slot for the phone's slot 2, and another time slot for the back-slot 3 battery pack. For example, if a phone is installed having a discharged battery pack then the charger station 1 will operate so as to direct all charging energy to the first slot 2 until such time that the phone's battery pack is detected as nearing or obtaining full charge. Referring to FIG. 2, this first charging period (referred to as a time slot for the phone 6) will contain a number of charging pulses. However, during this time no charging pulses and charging energy are directed to the back-slot 3. Charging energy is applied to the back-slot 3 only after the phone's recharged battery reaches a maintenance or trickle charge state, also referred to as a charger idle state. This second charging period is referred to in FIG. 2 as the time slot for the back-slot battery 5.
Referring now as well to FIG. 3, for a given PWM pulse it can be seen that there is a charger active period (defining some percentage of the charger current that is used) followed by charger inactive period (defining some percentage of the charger current that is not used). As the pulse width of the charger active period decreases the charger voltage decreases, typically down to some minimum specified voltage level, and consequently decreases the current that flows from the charger station 1 to the battery of the phone 6. Conversely, as the pulse width of the charger active period increases the charger voltage also increases up to, potentially, some maximum specified voltage level, as does the current flowing from the charger station 1 to the battery of the phone 6.
It can be appreciated that this results in wasted charging time, as the period between charging pulses (shown as a horizontal bar in FIG. 2 and as the charger inactive period in FIG. 3) is not used for charging any battery in either the phone's front-slot 2 or the spare battery back-slot 3.
As high speed data and other services begin to be supported by cellular telephones and personal communicators, their power consumption will increase as well, thereby necessitating the consumption of more battery power and hence more frequent battery charging cycles.
For example, before leaving the home or office a user may wish to recharge his phone's battery pack, as well as a spare battery pack for the phone. As can be appreciated, it is desirable for this recharging operation to be accomplished as quickly as possible so as not to delay the user's departure.